Full-duplex wireless transmission, in which transmission and reception can be simultaneously performed, includes the frequency division duplex (FDD) system that performs bidirectional transmission using different frequency bands for transmission and reception, and the time division duplex (TDD) system that uses the same frequency band for transmission and reception but divides the transmission and reception at a regular time interval and alternates between them. In Universal Mobile Telecommunication System (UMTS) Long Term Evolution (LTE), the cellular telephone standard, full-duplex wireless transmission by either the FDD system or the TDD system is used.
As a method of separating transmission signals and reception signals generally used in the RF front end of a UMTS LTE FDD transceiver, there is a system of connecting a power amplifier (PA) and a low-noise amplifier (LNA) with a duplexer. A duplexer is mainly manufactured using a surface acoustic wave (SAW) filter or the like in order to separate transmission signals and reception signals with a frequency-selective filter. Since the manufacturing process of a duplexer differs from that of a transceiver chip, a duplexer cannot be mounted within an integrated transceiver chip.
Another system is one that uses a circulator. A circulator is a something that makes the advancing direction of a signal one way. However, since a circulator utilizes the non-reversibility of phase rotation produced in a wave travelling in ferrite on which a DC magnetic field is impressed from outside, this also cannot be mounted in an integrated transceiver chip.
The same non-reversibility of ferrite can be realized using a gyrator circuit of an electronic circuit. By using a gyrator circuit, it is possible to implement the function of separating transmission signals and reception signals in an integrated circuit. For example, Patent Literature 1 discloses the gist of gyrator circuits functioning as a circulator in the case of satisfying predetermined conditions in a circuit in which they are cascade-connected with the same directionality in a loop.